1. Field of the Invention
This invention is related to the field of nuclear chemistry and in particular to the production of radioisotopes of selenium.
2. Description of the Prior Art
The radioisotope selenium-72 can be used as a radiopharmaceutical agent to diagnose a number of diseases. For example, selenium-72 is used in making a selenium/arsenic-72 generator. This generator has an application in medicine to diagnose a number of diseases with the use of positron emission tomography (PET).
One method for the production of selenium-72 and arsenic-72 is described in U.S. Pat. Nos. 5,204,072, 5,371,372, and 5,405,589 of Dennis R. Phillips. These patents describe a process wherein selenium-72 and numerous other isotopes are produced when a rubidium bromide target is irradiated with 800 MeV energy protons. The resultant selenium isotopes are electrolytically separated from the target (see D. R. Phillips, "Electrolytic separation of selenium isotopes from proton irradiated RbBr targets," Appl. Radiat. Isot., Vol. 38, pp. 521-525, 1987) or separated by precipitation or co-precipitation of metallic selenium by hydrazine dihydrochloride. There are number of shortcoming of this selenium-72 production process, including a multi-step complex radiochemical recovery procedure, a low production yield of selenium-72, a high level of selenium-75 and other impurity radionuclides, and the necessity of using a high energy proton beam to irradiate the target.
Another selenium-72 production method uses arsenic (As) or Cu.sub.3 As.sub.2 targets irradiated with 50 to 70 MeV protons. A multi-step procedure is again required to recover the selenium-72 (see R. Schwarzbach et al, "Production of Se-72 and Se-73 by medium energy protons," J. Labeled Compounds & Radiopharmaceuticals, Vol. 26, pp. 146-147, 1989). These targets have a low resistance to heat requiring irradiation by a low intensity beam. The process again requires a complex radiochemical procedure to recover the selenium-72 and results in a low yield.